MONTREAL, CANADA (February 5, 2002) -- Who says physicists don't have heart? In an effort to study the factors that lead to fatal cardiac rhythms, a team of Canadian researchers has shown that the importance of communication applies not only to people, but also to their heart cells. The researchers report their results in this week's issue of the journal Physical Review Letters.
Sudden cardiac death kills more than 250,000 people each year in the US alone. Physicists have been studying the important role that electricity plays in the heart's health--and how it may be a culprit in disease.
Electrical impulses regularly circulate through cardiac tissue and cause the heart's muscle fibers to contract. In a healthy heart, these electrical impulses travel smoothly and unobstructed, like a water wave that ripples gently in a pond. However, for reasons that have not been perfectly understood, these waves can sometimes develop into troublesome, whirlpool-like spirals of electrical activity that can circulate through the heart.
Investigating these "spiral waves," scientists at McGill University in Montreal studied chick-embryo cardiac cells grown as a sheet of tissue. In the first two days after this arrangement of cells is created, spiral waves often form in the tissue. When the researchers sprinkled the sheet of cardiac tissue with a drug that impairs communication between the cells, they observed that the rotating spiral waves broke up into multiple rotating spirals.
This breakup of spiral waves in the two-dimensional sheet is believed to be similar to the 3D electrical patterns that cause human hearts to undergo ventricular fibrillation, a potentially fatal cardiac rhythm that often occurs when communication between cells is impaired. In a real-world situation, reduced intercellular communication may be caused by a heart attack or by other cardiac diseases, which can produce diseased or damaged heart tissue.
Developing a simple computer model to explain their experimental findings, the researchers showed that electrical activity in cardiac tissue can spread like a fire in a forest. Like trees, cells "light up," or become electrically active, if enough neighboring cells display a sufficient level of electrical activity. When neighboring cells are able to interact or communicate strongly with one another, electrical waves quickly pass through the tissue, unobstructed; when interactions are weak, wave propagation is completely blocked. At intermediate levels of interaction, electrical waves break up into multiple spiral waves.
Understanding the effects of communication between cells provides insights into the electrical malfunctions that are suspected to lead to heart disorders, and may ultimately suggest strategies for avoiding them. In addition, spiral wave patterns, electrical and otherwise, appear in many other places in nature. The researchers' observations can help to explain the appearance of multiple spiral waves in the corrosion on metal surfaces, the aggregation of slime molds, and visually striking chemical reactions that display ever-changing patterns.
Source: Gil Bub, Alvin Shrier, and Leon Glass, " Spiral Wave Generation in Heterogeneous Excitable Media," 4 February issue of Physical Review Letters.
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